Problem: Simplify the following expression: $3\sqrt{45}$.
Answer: First, try to factor a perfect square out of the radical. $= 3\sqrt{45}$ $= 3\sqrt{9 \cdot 5}$ Separate the radical and simplify. $= 3\sqrt{9} \cdot \sqrt{5}$ $= 3 \cdot 3 \cdot \sqrt{5}$ $= 9\sqrt{5}$